strloin

strloin gives you copy-on-write (cow) slices of a string. If the provided ranges form a single contiguous region, then you'll get back a borrowed slice of the string. Otherwise, you'll get back an owned concatenation of each range.

use strloin::Strloin;

let strloin = Strloin::new("hello world");

assert_eq!(strloin.from_ranges(&[0..5]), "hello"); // borrowed
assert_eq!(strloin.from_ranges(&[0..5, 5..11]), "hello world"); // borrowed
assert_eq!(strloin.from_ranges(&[0..5, 6..11]), "helloworld"); // owned

Note that this crate is intended for cases where borrowing is far more common than cloning. If cloning is common, then it's likely that the performance overhead, much less the cognitive overhead, is too expensive and you should consider unconditionally cloning. Your mileage will vary. But, on a real-world text parser where 85% of from_ranges resulted in a borrow, switching from always cloning to conditionally cloning with strloin had the following impact:

Benchmark 1: always-clone
  Time (mean ± σ):      1.259 s ±  0.089 s    [User: 0.062 s, System: 0.063 s]
  Range (min … max):    1.082 s …  1.367 s    10 runs

Benchmark 2: strloin-slices
  Time (mean ± σ):     394.7 ms ±  40.0 ms    [User: 49.5 ms, System: 50.7 ms]
  Range (min … max):   310.7 ms … 452.0 ms    10 runs

Benchmark 3: strloin-ranges
  Time (mean ± σ):     376.5 ms ±  36.1 ms    [User: 45.5 ms, System: 56.5 ms]
  Range (min … max):   324.7 ms … 441.2 ms    10 runs

Summary
  'strloin-ranges' ran
    1.05 ± 0.15 times faster than 'strloin-slices'
    3.34 ± 0.40 times faster than 'always-clone'

Optional features

• beef - Swap out the std::borrow::Cow implementation for beef::lean::Cow. The performance difference in my use case was just noise, but it may serve you better.